Federal agents, military investigators and Texas Rangers are investigating whether the gun used in the Fort Hood massacre was purchased at the "Guns Galore" shop in Killeen, Texas, according to the store co-manager.

"They called last night and asked about a specific name and gun purchase, but the name was not Hasan," said the manager who gave only his first name, Dave. He said he did not want to reveal the name for fear it would compromise the investigation.

Three investigators, including one wearing a Texas Rangers badge, were seen entering the store just before noon Friday. The manager said they were interviewing all of the store employees.

They declined to comment as they left Guns Galore in a car with Department of Defense markings.

The manager said he recognized a photo shown to him of Major Nidal Malik Hasan, identified by authorities as the suspect shooter at Fort Hood. But he said Hasan would have had to show identification if he had bought the gun in his name.

The co-manager said the agents were interested in a FN pistol that uses 5.7 caliber ammunition.

The Associated Press, citing federal law enforcement sources, said the suspect used only one semi-automatic weapon in the attack.